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By Mike McClintock
Special to The Washington Post
Thursday, July 20, 2000; Page H04

The popularity of vinyl siding may have peaked, despite structural improvements that make panels stiffer and cosmetic improvements that make them look more like wood. The low-cost, low-maintenance alternative to wood and masonry is used on about 30 percent of new homes in the country--but that number has remained about the same since 1995.

On the plus side, you don't have to repaint vinyl every few years, and it's easy to clean. The overlaps in some panels can be staggered to look like butt joints in wood siding, and the molded clapboard shapes can create the traditional shadow lines you expect from solid siding. From a distance it can fool you unless you spot the give-away polyvinyl glare.

But sales pitches that started in the 1950s about space-age polymers lasting forever without cracking or peeling or fading have proven to be slightly optimistic.

You may not be able to spot every vinyl-clad house from the street. But closer up there is no mistaking the rubbery-looking surface, even if it is embossed with grain patterns modeled from solid wood siding or tinted with brown streaks that are supposed to make PVC look like clear-sealed wood but don't.

And if you touch it, vinyl bends because the standard siding is only 4/100 of an inch thick--less than the space between sixteenth-inch marks on a ruler. That makes it easy to cut (you can use a shears instead of a saw), but it may flex a bit much during installation.

The siding adds no structural value to the house; it simply clads the surface. In fact, the interlocking system is designed to hang somewhat loosely on partially driven nails, which can allow the panels to rattle in a stiff wind.

The siding also can't be fastened tightly because a typical length of PVC clapboard expands and contracts more than half an inch during temperature swings from cool nights to hot days.

That's one of the reasons you can buy so many variations of off-white and beige vinyl but not dark reds, greens and blues. The lighter colors reflect more sunlight and keep the siding cooler. Dark colors would make sunstruck siding even hotter and increase the chance of drooping, which actually is the first stage of melting.

The problem is significant enough that the Vinyl Siding Institute (VSI), a plastics industry trade group, warns against storing the siding on blacktop pavement during unusually hot weather, or under dark tarps without air circulation.

Lighter colors also resist fading better than dark colors, indirectly at least, because the bleaching effect of prolonged exposure to the sun would be more noticeable on a dark panel.

Durability

Early PVC siding was all vinyl. But to keep prices down and maintain popularity with cost-conscious consumers, manufacturers have gradually diluted the mix with inexpensive fillers.

The result is that many vinyls today are made with a utilitarian base and a concentration of quality features in the outer layer.

In some products, only the top 20 percent of the siding contains the more expensive ingredients that increase weather resistance and ultraviolet light protection.

Overall, durability is more a product of the installation than the material itself. But many of the advances in vinyl siding have gone into reducing the cost instead of making the product last longer.

For maximum durability, you can use thicker vinyl with reinforced joints. Although standard thickness is 4/100 of an inch, some companies offer siding that is 5/100 of an inch thick.

Thicker versions cost more, of course, in the $60-plus range per 100 square feet vs. the $35-plus range for standard products.

You also can strengthen a vinyl application by using panels with a rollover nailing strip. Standard panels have a small U-shape at the top (that's where the next panel hooks into place) and a single-thickness strip with perforated slots for nails. But some top-end products have a folded, double-thickness nailing strip and more material along the connecting seam. That makes the panels stronger and provides more holding power.

But even the sturdiest vinyl siding will look wavy if you install it on a wavy wall. That shouldn't be a problem on new construction, but can be if you're covering old siding.

The solution is to add furring strips that are shimmed over low spots to lie flat. That extra thickness of furring can make it difficult to trim existing windows and doors. But the wavy-wall problem causes the same kind of trouble with wood siding.

Installation and repair tips

Fasten trim pieces securely, but don't drive the siding nails all the way in. The VSI recommends leaving 1/3-inch of space under the nail head--about the thickness of a dime.

Center your nails in the horizontal slots provided in the nailing strip along the top of each panel. It will feel wrong when you're done (and you may hear some squeaking as panels shift in hot weather), but the siding should be loose enough to slide back and forth.

To remove a panel and make repairs, you first have to separate its interlocking seam. The tool of choice for this job is called a zip-lock tool, although some pros get by with the claw of a hammer. Snake the zip tool's can-opener head up into the seam, pry out and down, and then slide the tool along the seam to unlock the entire length.

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